Aurélien Gâteau

Indicators, notifications and co

written on Friday, September 18, 2009


Jonathan post about indicators has been received with various feelings, ranging from interest to questioning or plain hostility. Since I get more and more people asking about this indicator thing, I figured I should try to explain what indicators are, how they are different from notifications and answer a few other frequently asked questions.

Disclaimer: The opinions of this post are my own, they do not necessarily reflect Canonical position.

Indicators for the user

Indicators are a way to get permanent informations, rather than ephemeral ones like notifications. I find it easier to explain the difference with use cases.

Imagine you receive an incoming message from your IM client while you are away from your machine. A notification gets shown, but this notification goes away after a few seconds. You just missed it.

Since the IM client supports indicators, it also created an indicator for this incoming message. When you come back to your desk, you notice the spark on the indicator plasmoid. Clicking on the plasmoid popups a menu listing all indicator-enabled running applications. Below your IM application entry, there is an entry for this incoming message you received. You click the entry and the chat window is brought to the front.

You would also like to know if you have any unread message in this "From Boss" mail folder. So you look at the mail client entries, and notice that "From Boss" appears, with a count of 2. You click the "From Boss" entry and your mail client is brought to the front, showing the first unread message in the "From Boss" folder.

The "Indicator Display" plasmoid showing indicators from Kopete and KMail

You are now busy working on this report due to your boss for yesterday. You turned your status to "Busy, Do not Disturb, Will Bite", but that does not stop people from sending messages to you. If your IM client is smart enough, it can disable notifications and only create indicators. When your report is finally done, you can relax, click the indicator plasmoid and start chatting with the people who tried to reach you before.

Back home, you decide to spend the evening watching a movie on your laptop. Since you are running a fullscreen application, notifications are disabled: you do not want to get interrupted by this IRC message from your friend while Bruce Willis is busy saving the world. When world has been saved, you can click the indicator and catch-up with your friend.

Indicators for the application developer

libindicate-qt provides two objects for the application developer: QIndicate::Server and QIndicate::Indicator.

The application typically starts with instantiating a server, declaring its desktop file and "server type" (a way to group applications, for now the plasmoid only shows servers with the "messaging" type), then calling the show() method. As soon as this is done, an entry for the application appears in the indicator menu. When the user clicks on this entry, QIndicate::Server emits the serverDisplay() signal. All you have to do is to connect to this signal and bring your main window to front.

When an event worth mentioning to the user happens, you instantiate a QIndicate::Indicator for it. An indicator can have a few properties:

  • name: the text to display
  • icon: a QImage for your indicator
  • time: a QDateTime describing the time of the event, if relevant
  • count: an int representing a count, if relevant
  • draw_attention: a bool which must be set to true for the plasmoid to display its spark
"time" and "draw_attention" are useful for indicators representing events like IM messages, while "count" can be used for example by mail clients to create indicators for their folders.

When the user clicks on the indicator entry, QIndicate::Indicator emits a display(QIndicate::Indicator*) signal. Connect to this signal to perform the action relevant to this indicator.

(Note: the properties listed here are those used in the case of messaging communication, but the Indicator API is flexible enough to let you define other indicator properties)


Couldn't this be implemented within KDE notification system?

The KDE notification system can represent notifications in a few ways: showing popups, playing sounds, writing to log files, running programs...

I tried to implement support for indicators as a new way for the notification system to represent notifications, but it did not work because the notification system lacks the server/indicator structure. For example to implement the feature which brings the application to front when you click its entry, I ended up having to remember the window id of the first notification I received so that I could bring back this window. It was unreliable (what if the first window was gone by that time, or even not specified?) and it was not possible to do things like showing a count of unread emails in a folder for example.

Couldn't this be implemented with KNotificationItem?

KNotificationItem is a new xdg specification which aims at replacing the SystemTray specification. Quoting the specification itself: "It is intended to be complementary but not directly related with the Freedesktop's Desktop Notifications specification and is aimed as a replacement to the Freedestop System tray specification."

In short, it is system tray done right. It is a huge step forward as it makes it easier for the application/toolkit to implement system tray support and it makes it easier for the system tray host to display these icons in a way which is consistent with the rest of the desktop interface.

It expands on the system tray spec by introducing a notion of status (Passive, Active and NeedsAttention), a possible icon overlay and a category (ApplicationStatus, Communications, SystemServices and Hardware).

It has a few features indicators do not have, such as tooltips and support for right-click, middle-click and mouse wheel events.

It does not however provide an equivalent to the server/indicator structure, or to the "count" and "time" properties. This makes it impossible to implement indicators on top of KNotificationItem.

Still, the two systems have quite a few commonalities, so it may make sense to merge them in the future.

Where does it come from?

libindicate has been developed by Canonical Desktop Experience team, as part of the Ayatana initiative. Ubuntu 9.04 (Jaunty) was the first version of Ubuntu to feature it on the GNOME desktop.

The upcoming Ubuntu 9.10 (Karmic) expands on this by providing a Qt binding for libindicate, adding support for indicators to a few Qt and KDE applications and a plasmoid to display indicators on the KDE desktop.

Is it Ubuntu specific?

No. The Canonical Desktop Experience team considers itself as an upstream developer team. As such we release source tarballs, which are then packaged by Ubuntu, but can be packaged by other distributions as well.

Here are the links to download them:

Does it depend on GTK+?

libindicate-qt depends on libindicate. libindicate used to depend on GTK+ at runtime, but it's not the case anymore.

It still depends on GTK+ at build time because compiling libindicate from source produces and depends on GLib, but does not depend on GTK+. I recon depending on GTK+ to build the library is a problem for source-based distribution like Arch Linux or Gentoo, patches from autotools masters are welcome. A bug has been filled to track that issue.

It is a cross-desktop system: indicators from KDE applications show up in GNOME indicator applet, indicators from GNOME applications show up in KDE plasmoid.

What applications support it?

On the KDE side:
  • Quassel
  • KMail
  • Konversation
  • Kopete
Upstream processes for these patches are in various states. Quassel patch is already in their git repository, Konversation patch has been submitted but needs some work, KMail and Kopete patches have not been submitted yet.

You can find all the patches here.

On the GNOME side:

  • Evolution
  • Gajim
  • Gwibber
  • Pidgin

What is the difference between the "Indicator Display" plasmoid and the "Incoming Message" plasmoid from kdeplasma-addons?

Both plasmoids have the same goal, but the "Incoming Message" plasmoid tries to implement this goal with application-specific code: it has specific code for Evolution, KMail, Pidgin, Kopete and XChat. The "Indicator Display" plasmoid on the other hand relies on applications to use libindicate and does not contain any application-specific code.

This post was tagged ayatana, faq, indicators, kde, notifications and plasmoid